An Iranian university professor working at a top nuclear facility was killed in Tehran Wednesday — the third killing in a string of attacks on scientists working on the country’s nuclear program.

Two men on a motorcycle attached a magnetic bomb to Mostafa Ahmadi Roshan’s car outside the campus of Allameh Tabatabai University, killing him and his driver in what the country has described as a ‘terrorist act,’ state media reported.

A passerby was wounded and remains in hospital.

State news agency Islamic Republic News Agency (IRNA) said Roshan, 32, a chemistry expert and the director of the Natanz uranium enrichment facility in the Isfahan province had “organizational links” to the country’s nuclear agency.

The morning attack mirrors at least three other attacks on scientists since early 2010 — leaving analysts to suggest the assassinations are part of a widening Allies-led operation to halt Iran’s atomic program.

The U.S. and its allies of Britain and Israel are pressuring Iran to suspend uranium enrichment, a key element of the nuclear program that they suspect is aimed at developing nuclear weapons technology.

While low levels of uranium enrichment can be used as nuclear fuel, at higher levels it can be used as material for a nuclear warhead.

Natanz is Iran’s main enrichment site, but Iranian officials said earlier this week that they are expanding some operations to an underground site south of Tehran.

Iran denies the allegations of nuclear weapons production, saying its program is intended for energy and medical research, specifically the production of medical radioisotopes to treat cancer patients.

Iran has accused the U.S and its allies of engaging in a “terrorism” campaign against its nuclear program.

The U.S., Britain and Israel have denied the accusations.

However, on Tuesday Israeli military chief Lt. Gen. Benny Gantz told an Israeli parliamentary panel that this year would be a “critical year” for Iran — mainly for “things which take place in an unnatural manner.”

“Many bad things have been happening to Iran in the recent period,” added Mickey Segal, a former director of the Israeli military’s Iranian intelligence department.

“Iran is in a situation where pressure on it is mounting, and the latest assassination joins the pressure that the Iranian regime is facing.”

Israel declined to comment on the Wednesday attack.

The U.S. said it “had absolutely nothing to do” with Roshan’s death. Secretary of State Hillary Clinton denied any U.S. involvement in the killing.

White House spokesman Tommy Vietor said the U.S. condemns “all acts of violence, including acts of violence like what is being reported today.”

Reports said two assailants on a motorcycle attached a magnetic bomb to Roshan’s car, killing him and his driver Wednesday. Roshan was a chemistry expert and director of the Natanz uranium enrichment facility in central Iran.

A similar bomb to Wednesday’s exploded Jan. 12, 2010 killing Tehran University physics professor Masoud Ali Mohammadi. He was killed when a bomb-rigged motorcycle exploded near his car as he was about to leave for work.

In November 2010, twin bomb attacks in different parts of the capital killed nuclear scientist Majid Shahriari and wounded scientist Fereidoun Abbasi.

Shahriari was a member of the nuclear engineering faculty at Shahid Beheshti University in Tehran and co-operated with the Atomic Energy Organization of Iran. He was an expert in neutron transport a method at the heart of nuclear chain reactions in reactors and bombs.

Abbasi, a specialist in nuclear isotope separation, was appointed head of Iran’s atomic agency after the attack.

In July 2011, motorcycle-riding gunmen killed university student Darioush Rezaeinejad.

State media first reported him as a scientist involved in alleged attempts to make nuclear weapons but later identified him as an electronics student.

In November 2011, 17 people, including Major Gen. Hasan Moghaddam, a prominent figure in Iran’s nuclear program, died in an explosion at an ammunition dump near Tehran. Iran later said the incident was an accident.